1. Field of the Invention
This invention refers to a precision clamping unit for an injection molding machine. The molding machine has a machine bed on which are positioned stationary and sliding guided mod clamping plates and at least one drive for moving and locking the mold clamping plates.
2. Description of the Prior Art
The market volume for precision injection molding components, such as computer peripherals, copying machines, photography equipment, telecommunications equipment and optical storage equipment has recently increased. The machines which are suitable for molding components must possess special characteristics, such as firmness of form with parallelism of the mold clamping guide, as well as firmness of form in areas where only marginal clamping forces are present, as well as to be adapted for precision injection.
Injection molding machines are known where the moveable mold clamping plates are guided by a transom or beam and moved by one or more drives which consist of a servo-motor and a ball spindle or screw drive. This type of machine has replaced the customary movement drives of mold clamping plates which, previously, had toggle joints, hydraulic cylinders, ball spindles and servo-motors because of the precision of movement provided thereby. The disadvantage of such machines, however, is that parallel guidance of the molding clamp plate on a beam is not precise, because the beam sleeve guides cannot be made with acceptable tolerances.
U.S. Pat. No. 3,208,135 discloses an injection molding machine where the mold clamping plate rides on chains operated by hydraulic motors which, in turn, drive screw spindles and associated nuts. This type of drive has play and tolerances which make synchronism impossible.
Another injection molding machine for plastic is disclosed in French Laid Open patent appln. No. 25 16 857. This device has the disadvantage that component forces can be exerted and, if they are higher than the weight of the plate in the device, can lead to vertical disalignment of some of the components of the device.
Another disadvantage of the above-mentioned machines is that the electric drive units which are utilized have small power density and do not permit a compact design of the machine. It was attempted to generate the required higher capacity through the parallel switching of two electro-motors, however, the results were not satisfactory.